Site Characterization Technologies for DNAPL Investigations

Site Characterization Technologies for DNAPL Investigations

ACEC Meeting December 8, 2004

Linda Fiedler Environmental Engineer

Technology Information and Field Services Division

Office of Superfund Remediation and Technology Innovation

US Environmental Protection Agency fiedler.linda@epa.gov

Site Characterization Technologies for DNAPL Investigations

cluin.org

Site Characterization Technologies for DNAPL Investigations

• Published Sept. 2004 • Summarizes challenge of finding/delineating

DNAPL in subsurface

• Gives inventory of “technology toolbox” currently available to characterize DNAPL

• For each, Includes description, uses, drawbacks, and short case studies

cluin.org 11/18/04 2

Geophysical TechniquesGeophysical Techniques

• Used to survey large areas or describe small-scale conditions, such as those in and around borehole walls

• Measure physical properties of subsurface materials • Changes in measurements may indicate changes in

subsurface matrix (e.g., stratigraphy that locates preferential pathways for DNAPL migration)

• Report categories include: – Borehole methods – Electrical methods – Electromagnetic methods – Ground penetrating radar, – Magnetics

– Seismic

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NonGeophysical TechniquesNonGeophysical Techniques • Other techniques shown to have some success in

characterizing DNAPL sources and gaining access to subsurface strata where DNAPLs may be found

• Report categories include: – Diffusion sampling – Direct push technology equipped with tools to take

depth-discrete samples/measurements along vertical axis (e.g., conductivity probe, induced fluorescence, membrane interface probe)

– In situ groundwater sampling (depth-discrete) – Hydrophobic dyes (e.g., Sudan IV dye) – DNAPL partitioning tests (e.g, PITT) – Soil gas profiling

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Report ConclusionsReport Conclusions

• Growing range of field-based tools to locate and characterize DNAPLs in wide variety (but not all) settings

• Some methods take direct chemicalmeasurements, others measure physical site characteristics

• In many cases DNAPLs can be found by using correct mix of tools for site-specific conditions (i.e., line-of- evidence approach)

• Effective application of field methods requires systematic planning and dynamic workplanning (i.e., the 3 legs of Triad approach) to allow in­field refinement of site conceptual model

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VINT HILL FARMS STATION, VIRGINIA

DNAPL Site Characterization Utilizing Membrane Interface Probe (MIP) and Direct Sampling Ion Trap Mass Spectroscopy

Background

• Elevated PCE/TCE levels detected in latter stages of property transfer at closed Vint Hill Farms Army installation

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Preliminary CSM From Systematic Planning Outline

• Volatile organic compound (VOC) contamination in saturated overburden - 0.5 acre area

• Overburden GW flows NW (<0.4 ft/year) • VOC contamination is sporadic, apparently

resulting from one or more small spills of solvent • Fractured bedrock aquifer also contaminated

with VOCs

• Production well located 400 ft downgradient of bedrock aquifer contamination has not been impacted

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Tool Box Including Real-Time Measurement Systems

• Membrane Interface Probe – Soil Sampling –Electron Capture Detector (ECD) –Photoionization Detector (PID) –Trapping of gas stream for speciation

• Passive Diffusion Bags (PDBs) - GW –Temporary wells (1-inch inner diameter)

• Soil samples from Geoprobe borings • On-site field laboratory – DSITMS (MIP gas

stream, groundwater, soil)

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Principles of MIP Operation

• Heated probe • Semi-permeable

membrane • Contaminant vapors

partition into acarrier gas

• Transported to FID,PID, & ECD detectors at the surface

• Results are

time on a lap-top computer.

displayed in real-

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Advancement of MIP Using Geoprobe Rig

until equilibrium isreached

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Passive Diffusion Bag Sample Collection • Chemicals diffuse from

high to low concentration

• Multiple PDBs w thin well screen determine vertical stratification

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Dynamic Work Plan

• Allowed project to adapt in real time (while crew still in the field) to new information as it became available

• Provided framework for preliminary Conceptual Site Model (CSM) to be tested and modified in the field

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Data Management and Communication During Systematic Project Planning andDynamic Work Plan Development:

• Frequent teleconferences • On-site pre-mobilization meeting to finalize the

Dynamic Work Plan

During One-Week Dynamic Field Effort:

• Rapid dissemination of field data using project web-site (with 3-D data visualization) – data posted nightly

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Sampling Conducted During Triad Investigation (November 2003)

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Sample MIP Log – MW34-4(2)-MIP

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AREE 34 MIP ECD Responses

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Triad Investigation (November 2003) DSITMS Temporary Well Analytical Results –

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(µ

()

µ

H14-MIP ECD Log

(µV)

(t)

DSITMS Soil Results vs. MIP ECD Response at H14 DSITMS Soil Results

Total VOCs g/kg)*

Depth fee t

*Assumes non-detected compounds at 0 g/kg

Response

Depth fee

Selected Findings of Triad Investigation

• No source of greater VOC contamination upgradient of MW34-4

• Extent of the highest VOC contamination appears to be very limited and occurs within the finer grained soils (7.5 to 13 ft bgs)

• MIP ECD sufficiently sensitive to identify contaminated and “clean” areas

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Triad Investigation Objectives Achieved

• CSM confirmed with high degree of confidence - two or more small sources of contamination over a 0.5 acre area

• Triad approach allowed rapid completion of site characterizationactivities that had been ongoing forseveral years

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152

IW

A

RS0048

Site Characterization for Chlorinated NAPL

Remediation East Gate Disposal Yard

Fort LewisWashington

I would like to recognize the people who helped make this NAPL characterization effort successful.•Public works at Fort Lewis – Rich Wilson the installation Project Manager•Corps Team (Kira Lynch, Bill Goss, and Jeff Powers).•Contractors: URS, GSA, TEG, Cascade Drilling/Boart-Longyear.

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EGDY History

•

•

and POLs. • Di in

free liquid or burned.

Received Logistics Center wastes from 1946 – 1970’s. Cleaning and degreasing solvents

sposedtrenches in drums,

•The Logistics Center began operations in 1941 as the Quartermaster Motor Base and was later renamed the Logistics Center. •The primary mission of the Logistics Center has been vehicle maintenance throughout its operational history. •TCE was used as the degreasing agent of choice up until the 1970’s. •Mixed solvent/petroleum hydrocarbon, oil and lubricant waste were generated. •These wastes were reportedly transferred to the EGDY in drums and buried in the trenches. Drums may have been crushed during the operations or left intact. It was also reported that liquid wastes were poured directly into trenches and used to burn woody debris. Liquids may also have been poured directly into open trenches and subsequently buried.

Conceptual Site Model

• Primary COC waste degreasing agent,mineral spirits, and waste oil – TCE, Cis-1,2-DCE, TCA, PCE, TPH

• GW at approximately 10 feet bgs

• Complex hydrogeology

• NAPL varies in density and is found as LNAPL and DNAPL – DNAPL confirmed to 55 feet bgs

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250 100 200 300 400

Feet

0 100 200 300 400

Feet

Aerial Photo Analysis Results

•An analysis of aerial photographs of the site from the early 1940’s through the 1980’s was performed to determine the locations of trenches and pits used for disposal.•Both open trenches and linear scars were used to identify disposal locations.•The red shapes in this figure represent the approximate extent of trenches or pits identified from aerial photos.•The analysis of the aerial photos was used to defined boundaries of the investigation.•Because it was difficult to distinguish some trench scars from vehicle tracks and because portions of the area were sometimes regraded between photo events, an area somewhat larger than the area containing only trenches was included within the investigation boundary.•This boundary set the limits of the area requiring a geophysical survey.

260 100 200 300 400

Feet

EM-61 Survey Results

•An electro-magnetic survey was performed within the investigation boundary to locate trenches with metallic debris. •The EM-61 method generates rapid EM pulses into the subsurface to measure the prolonged response from metallic objects versus shorter natural response.•A closely spaced 2.5 x 5 foot grid over a the 35 acre area produced excellent results that clearly revealed narrow linear features.•The location of metallic debris matches closely with the locations of trenches identified from aerial photographs.•However, the EM survey revealed metallic debris in some areas that were missed in the aerial photo analysis due to lack of aerial photos when these features were visible.•The combined aerial photography and EM-61 survey results were used to guide the initial sampling locations of the soil gas, trenching and groundwater methods.

270 100 200 300 400

Feet

Soil Gas Sampling

•Soil gas samples were collected to try to determine the approximate location of NAPL sources in the vadose zone.•45 locations were sampled from a depth of 5 feet.•Results were mixed. Some high VOC results, but most were uniformly low. Method only seemed to work if sample collected right at an area later confirmed to have NAPL. Area was too large to cost effectively blanket all suspected trenches with soil gas sampling locations so this method was discontinued.•Results of soil gas sampling were used to direct the locations of some of the exploratory trenches.

280 100 200 300 400

Feet

Exploratory Trenching Results

•Trenching results were added to the growing CSM.•Groundwater drive point locations based upon trench, aerial and geophysical results.

290 100 200 300 400

Feet

Drive Point Groundwater Results

•Three major hotspots identified where TCE containing NAPL likely present based upon greater than 10,000 ug/l in groundwater detected. •A fourth area of less contaminated groundwater, but above 1,000 ug/l also encountered where NAPL likely present in lesser amounts than the other three areas.•The three major NAPL areas were selected as areas where NAPL remediation efforts should be focused.•Mention groundwater flow direction.

300 100 200 300 400

Feet

Drum Removal Results

Superimpose drum locations on NAPL evidence map.•Locations of drums containing NAPL were plotted.•Circles represent locations where one or more NAPL containing drums were located.•This combined lines of evidence map was used as the basis for the planning of the Phase II investigation.•The Phase II investigation was designed to fill data gaps associated with the EE/CA proposed remedies for the source area.•Detailed logging of vadose zone NAPL.

310 100 200 300 400

Feet

MIP Results

•NAPL was identified at the locations with solid triangles. Open triangles indicate no NAPL present based upon MIP results.•Sonic cores were required to fill in the horizontal and vertical data gaps left from the MIP. •The locations of sonic borings were used to compliment, not replace the MIP data.

320 100 200 300 400

Feet

Sonic Drilling Results

•Sonic boring quantity, locations and depths were determined in the field.•Sonic gave excellent NAPL ID results.

330 100 200 300 400

Feet

Selection of Treatment Volumes

•Combined lines of evidence used to select the NAPL thermal treatment volumes.•Sonic and MIP used primarily to determine limits of three main NAPL areas for thermal treatment, but extent of trenches containing drums and evidence of possible liquid waste disposal in NAPL area 2 from historical aerial photographic analyses also considered.

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EGDY NAPL TREATMENT AREAS

Lessons Learned

• ‘Toolbox’ Approach needed at this stage of tool development

• Treatment area could potentially have been refined if flux assessment had been conducted prior to definition of treatment areas

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Characterizing Down Volume to Be Treated

• Solvents Recovery Services of New England (SRSNE) NPL site - Large site w/ as much as 1M gallons of solvent/PHC contamination

• Initial (early 90’s) situation - lack of effective remedies and estimates of 400,000 cubic yards led discussions in direction of Technical Impracticability (TI) waiver

• Recent Developments - Advent of effective source removal/reduction options (e.g., in situ thermal) led to further site characterization

– New borings combined w/ existing data resulted in downward volumetric revision to 42,000 cubic yards

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Conceptual Site Model Evolves Through Remedy Implementation • S California wood treater – Alhambra, Ca

– Initial site characterization on 100’ centers

• In Situ Thermal remedy heater wells installed on 5-7’ centers – i.e., x20> spatial resolution – Wells installed 2’ below estimated bottom of

contamination found additional contamination – Treatment volume adjusted to reflect new data

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